As the world's demand for fossil fuels increases, energy companies find themselves pursuing hydrocarbon resources located in more remote areas of the world. Such pursuits take place both onshore and offshore. One type of fossil fuel is natural gas. The phrase “natural gas” usually refers to methane. Natural gas may also include ethane, propane, and trace elements of helium, nitrogen, CO2, and H2S.
Natural gas in commercially available quantities is often found in locations remote from existing natural gas markets. Thus, it is necessary to transport the natural gas great distances. This is oftentimes done by means of tankers that cross large ocean bodies.
To increase the volumetric capacity of a tanker with respect to the gaseous commodity being transported, it is known to liquefy the natural gas. Liquefaction is done by cooling the gas-phase product to condense it into a liquid phase. This, in turn, reduces its volume for economic transportation to a distant market.
A condensed natural gas product is typically referred to as liquefied natural gas, or “LNG.” LNG takes up about 1/600th the volume of natural gas in the gaseous state. LNG is generally odorless, colorless, non-toxic and non-corrosive. Specialized LNG vessels have been designed to transport LNG. In addition, LNG terminals have been erected that receive the offloaded LNG and vaporize it back to its natural gas state. In some instances, the offloaded LNG is stored in tanks on or near shore or in underground reservoirs. In other instances, the offloaded LNG is released into a natural gas transmission grid for the existing natural gas market.
In the area of original production, the liquefaction process is carried out in a LNG plant, which may be very capital-intensive. Large refrigeration units are required to bring natural gas down to a temperature needed for phase change into a liquid state. In the case of methane, the condensation point is approximately −162° C. (−260° F.).
In an LNG plant, one or more refrigerant streams are placed in heat exchange with the natural gas in production. The refrigerants typically are pure component hydrocarbons such as methane, ethane, ethylene, propane, a butane, a pentane, or a mixture of these components. Nitrogen may also be used in a blend. The very large sizes of LNG liquefaction plants make for some of the lowest unit-cost cryogenic refrigeration systems in the world.
LNG plants rely on large compressors. In most LNG plants, the refrigeration compressors are directly driven by large gas turbine engines. The plants may employ generators to provide electrical power for electric motors driving smaller loads. The compressors and the generators require significant power generation and a considerable distribution system.
It is also noted that many of the reservoirs currently in production and available for the processing of liquefied natural gas are in relatively deep waters. Such waters tend to be remote from land. To reduce the infrastructure and costs of transporting produced gas to shore, the LNG industry has considered the development of floating, LNG processing plants. In this instance, the natural gas would be chilled on location, and then offloaded directly onto an LNG tanker for immediate transport.
One of the challenges associated with such an offshore project relates to the space and weight requirements of the very large LNG production facilities. Placing such large facilities onto the deck and into the hull of a ship may not be commercially feasible. The alternative is to erect a platform using, for example, structural steel. This too requires significant infrastructure costs.
LNG receiving terminals and regasification facilities can also be either off shore or on shore and require pumps and other rotating equipment. These facilities often have stand alone power generation equipment or are built next to a power generation facility that utilizes the natural gas as a fuel source for producing electric power through a gas turbine and generator possibly including combined cycle power generation.
A need therefore exists for a gas processing plant, power plant, LNG receiving and regasification facility that utilizes equipment having a smaller footprint than currently-utilized gas processing components. A need further exists for a gas processing plant, power plant, LNG receiving and regasification facility that utilizes components having a higher efficiency in the utilization of electrical power, resulting in reduced fuel demand and lower greenhouse gas emissions.